This invention relates to automatic shutoff valves, particularly of the type used for beer dispensers.
The dispensing of beer, as well as similar operations for soft drinks and other liquids, employs compressed gases, carbon dioxide in the case of beer and soft drinks. Typically there is a large container, such as a beer keg, containing liquid. A tube extends from the top of the container to near the bottom thereof. There is a special coupling at the top of the container which admits the pressurized gas and allows the liquid to be discharged from the tube. In the case of beer, the coupling is typically connected to a tap at the bar by means of a long hose.
Problems are encountered however when the container is empty or near empty. Eventually the level of liquid drops below the bottom of the tube in the container. This causes gas to be forced out the tube, through the hose and to the tap at the bar. The container is then replaced with a full keg of beer or the like, but foaming occurs until the hose has been purged of gas by a fresh supply of liquid. This causes a considerable loss of time at the bar in pouring out the foam and wastage of beer which has been converted to the foam.
Automatic shutoff valves has been devised to stop the flow of fluids from the container once the supply of beer or other liquid in the container has been exhausted. An example of such a valve is found in the U.S. Pat. No. 3,587,927 to Stott. These valves include a chamber, typically a transparent one, which has a float therein. There is a valve member on the bottom of the float. There is an opening in the chamber for admitting liquid from the container. The valve has an outlet for the liquid which is connected to an opening located in a valve seat at the bottom of the chamber. When the chamber is full of liquid, the float rises above the bottom of the chamber, allowing the liquid to be discharged through the opening at the bottom of the chamber toward the outlet. However, when gas is received from the container into the chamber, the float is no longer supported and drops, allowing the valve member to close the opening and preventing further fluid (gas or liquid) from being discharged from the valve.
However, certain problems have been encountered with prior art automatic shutoff valves of this type. Often these valves seem to work satisfactorily when used only intermittently. However, under some conditions they have been found to stop functioning satisfactorily, preventing an outflow of liquid from the container even when the container is not empty. These problems usually arise when the liquid is dispensed quickly and repeatedly. This occurs, for example, in bars dispensing high quantities of beer.
One reason why this has occurred is that, under the conditions discussed above, the float can be sucked down towards the valve seat, causing the valve member to close off the valve seat and stopping the flow of liquid. This can occur, for example, when the flow of liquid is repeatedly stopped and started, for example due to turning the tap on and off at the bar in the case of beer dispensers. It is believed that this practice causes the float to bob up and down. The inertia of the float in the downward direction, together with the suction created by the liquid being discharged from the bottom of the chamber, can bring the float close enough to the valve seat so the valve member becomes jammed therein. Once this occurs, the pressure of liquid entering the chamber from the container keeps the valve member in place and prevents a further outflow of beer or other liquid.
In order to alleviate this problem, it has become a practice to make the chambers of the valves vertically elongated such that the float floats well above the valve seat and the discharge opening during normal operation. In this way, the valve member does not come close enough to the valve seat to be sucked into it.
However this has lead to another problem. These relatively long automatic shutoff valves are then too high to fit under many counters, for example, when installed on the top of a beer keg. Moreover, they are subject to damage when connected to a keg of beer, or other container, if installed thereon. Accordingly, many such automatic valves are mounted at a position remote from the container, such as on a wall, and connected to the container by a hose. This is disadvantageous because it means that gas can fill this hose before the flow of liquid is stopped by the automatic shutoff valve. When the keg of beer, or other container, is replaced, the gas in this hose must still be purged before normal dispensing can recommence.